The manual wheelchair user controls the wheelchair with the hand rims. The wheelchair hand rim is typically a tubular hoop rigidly attached to the outside of the wheel. The hand rim, or handrim is known by several different names, including pushrim, handring, and handrail. Most hand rims in use today are made from steel or aluminum tubing that has been formed into a hoop with the ends welded together. The hand rim is mounted offset from the wheel to allow space for the user's hand to grip around it. Hand rims enable the wheelchair user to propel forward, turn, and brake. When propelling forward, the user reaches back, grips both hand rims tightly and pushes forward until his/her arms are almost fully extended. The user then releases the hand rims and begins preparing for the next push. Braking is accomplished by lightly gripping the hand rim as it slips through the user's hand. The tighter the grip, the greater the deceleration. The user generally maintains a fixed arm posture during braking.
Since wheelchair users rely on their upper extremities for mobility, pain and injuries to the upper extremity can severely impact function and independence. Unfortunately, there is a high occurrence of upper extremity repetitive stress injuries in the manual wheelchair user population. In a study of 130 manual wheelchair users, 59% were found to have upper extremity pain (Dalyan, et al, “Upper extremity pain after spinal cord injury” Spinal Cord vol. 37, 191-5, (1999)). Development of repetitive stress injuries has been associated with the loading applied to the hand rim during wheelchair propulsion. In particular, impact loading that occurs at the beginning of the push (Boninger, et al, “Wheelchair pushrim kinetics: body weight and median nerve function” Archives of Physical Medicine and Rehabilitation vol. 80, 910-5, (1999)), and peak loading on the hand rim (Boninger, et al, “Shoulder imaging abnormalities in individuals with paraplegia” Journal of Rehabilitation Research and Development vol. 38, 401-8, (2001)) have been identified as adverse conditions. Results of these studies suggest that reducing the demand on the user during propulsion may prevent or delay the development of injuries.
The typical hand rim in use today is functionally equivalent to that disclosed in U.S. Pat. No. 4,687,218 (issued to Okamoto on Aug. 18, 1987). In this design, the hand rim is attached to the wheel using machine screw fasteners passing through rigid standoffs spanning between the wheel and the hand rim. The rigid standoffs typically create a 0.75 inch clearance space between the wheel rim and the inside edge of the hand rim. As an alternative to the rigid standoffs, hand rims are also similarly attached to the wheel using welded metal tabs. Hand rim hoop diameters are normally proportional to the size of wheel onto which the hand rim is mounted. Hand rims commonly have a tubing diameter of about 0.75 inches. While generally suitable for propelling and maneuvering the wheelchair, conventional hand rims have some inherent disadvantages.
For example, the relatively small tubing diameter of the hand rim provides a very small gripping surface for the user. As such, the pressure against the user's hands on the hand rims is relatively high as the user pushes down on the hand rim with sufficient force to propel or otherwise maneuver the wheelchair. For many users, this level of pressure against the hands may be uncomfortable or even painful.
Hand rims are generally smooth with poor frictional properties. As a result, users need to grip hard to prevent slipping when pushing the wheelchair. These properties are due to the need to avoid abrading or burning of the hands during braking. Heat is generated as the hand rim slides through the hand during braking. Hand rims are typically made of a metal that has relatively high heat transfer characteristics, such as aluminum or steel, which serves to evenly distribute the heat over the entire hand rim. High friction coatings for hand rims, such as vinyl or foam are commercially available and have been found to significantly reduce physical demand for pushing (Richter and Axelson, “Effect of a vinyl-coated handrim on wheelchair use” Proceedings of the American Society of Biomechanics Conference 2003). Unfortunately, since the high friction coatings are heat insulators they result in a rapid local heat buildup at the hand/hand rim interface, making them unsuitable for sustained braking.
It is known, that there is an impact force as the hand strikes the hand rim in the beginning of the push. This impact force has been associated with the development of repetitive stress injuries among wheelchair users (Boninger, et al, “Wheelchair pushrim kinetics: body weight and median nerve function” Archives of Physical Medicine and Rehabilitation vol. 80, 910-5, (1999)).
There are numerous alternative hand rim designs. Some of the designs target improved manufacturability, while others attempt to improve hand rim ergonomics. There are several patented designs that integrate the wheel rim and the hand rim as a single extruded part, including U.S. Pat. No. 2,938,738 (issued to La Rue on May 31, 1960), JP Patent Number 7304302 (issued to Hashimoto on Nov. 22, 1995), and JP Patent Number 9193602 (issued to Hashimoto on Jul. 29, 1997). While these designs may serve to improve manufacturability, they do not address the ergonomic disadvantages of the standard hand rim.
DE Patent Number 3834696 (issued to Heinemann on Apr. 18, 1990) and U.S. Pat. No. 4,366,964 (issued to Farey on Jan. 1, 1983) describe hand rims with various cross-sectional shapes in an attempt to better match the shape of the hand during the grip. While improvements in grip comfort are important, these designs do not address the issues of low friction and impact loading during use.
Then, there is a collection of designs that detail methods to integrate a high friction surface into the hand rim without the associated problems of burning of the hands during braking. The general approach in all these designs is to provide a high friction material on the top surface of the hand rim and retain the high heat transfer metal on the bottom surface. In U.S. Pat. No. 5,927,739 (issued to Evling on Jul. 27, 1999), a standard hand rim is fitted with a rubber strip embedded along the top surface. In U.S. Pat. No. 6,241,268 (issued to Niklasson on Jul. 5, 2001), a contoured cross-sectional shape is coated with rubber along the top surface. U.S. Pat. No. 6,276,705 (issued to Baldwin on Aug. 21, 2001) is similar to U.S. Pat. No. 6,241,268 (issued to Niklasson on Jul. 5, 2001) except in this design, the shape of the hand rim is not contoured and a second hand rim of smaller hoop diameter is mounted concentrically within the primary hand rim hoop. While all of these designs attempt to improve frictional characteristics for pushing, they do not reduce impact loading during propulsion. In addition, all of the designs described above require the wheelchair user to alter his/her method of braking. Normally the user brakes by pinching across both the top and bottom surfaces of the hand rim. Since the top surfaces of the hand rims have a high friction heat insulating coating, the user cannot grip on the top surface when braking. Instead, the user must pull up on the bottom surface of the hand rim, which is more difficult to do and control than the standard braking technique.
U.S. Pat. No. 6,120,047 (issued to Axelson on Sep. 19, 2000) details an approach to addressing the ergonomic disadvantages of the standard hand rim wherein the rigid fasteners connecting the hand rim to the wheel are replaced with shock absorbing resilient fasteners and frictional characteristics are improved by introducing a dual hand rim system, where the inner hand rim is coated with a high friction material and the outer is left uncoated for traditional braking. While this design addresses the target ergonomic issues, there are some disadvantages, including: 1) in order to reduce the impact, which occurs locally between the hand and the hand rim, the entire hand rim must displace relative to the wheel rim, 2) the frictional benefits rely on the use of the dual-hand rim system, which requires two hand rims, equating to additional weight and cost, and 3) the shape of the handrim does not conform to the shape of the hand when gripped, resulting in peak pressure points on the hand during use.
Accordingly, there is a need for an ergonomic hand rim device for a manual wheelchair wheel, which overcomes or substantially alleviates the problems associated with prior designs.